A Mid-Infrared Narrowband Absorber Based on a Subwavelength Fine-Structured Silicon-Gold Metagrating

A subwavelength fine-structured silicon-gold metagrating was designed for realizing mid-infrared (mid-IR) narrowband absorbers. The metagrating consisted of a silicon grating on the stack of a gold film and a quartz substrate. The silicon grating consisted of two periodically arranged silicon strips in each unit cell. The numerical results reveal that perfect absorption of the traverse-magnetic (TM) polarized light at a wavelength of 4.071 mu m can be achieved, with an absorption rate of similar to 99.2% and an absorption full-width at half-maximum (FWHM) bandwidth of similar to 31 nm. Thus, the proposed structure is useful for the spectral control of mid-IR signals. When used as a refractive index sensor, the structure has a measuring range of 1.0-2.0 with a quasi linear response, with a figure of merit (FOM) of similar to 103.